Why is my movement so slow and stuttering inconsistently?

As the title says, my movement is incredibly slow for what it should be and stuttering inconsistently.

I want to make a 3D platformer with tight controls and figure the best way to do that is by setting the velocity directly to the rigidbody.

I’m only using one script on a capsule for testing purposes. Here’s the script.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.InputSystem;

public class PlayerController : MonoBehaviour
{
    [Header("References")]
    [SerializeField] Rigidbody rb;
    [SerializeField] PlayerInput input;

    #region Input Variables
    bool jumpPressed = false;
    bool boostPressed = false;
    bool movePressed = false;
    Vector2 moveInput;
    #endregion

    #region Physics Variables
    float groundedGravity = -0.5f;
    [SerializeField, Range(1f, 5f)] float standardSpeed = 2f, boostSpeed = 2f;
    [SerializeField, Range(10f, 20f)] float maxSpeed = 10f;
    Vector3 appliedMovement;
    #endregion

    #region General Functions
    void Awake()
    {
        rb = GetComponent<Rigidbody>();
        input = new PlayerInput();

        rb.useGravity = false;
        appliedMovement = new Vector3();

        input.player.move.started += OnMove;
        input.player.move.performed += OnMove;
        input.player.move.canceled += OnMove;

        input.player.jump.started += OnJump;
        input.player.jump.canceled += OnJump;

        input.player.boost.started += OnBoost;
        input.player.boost.canceled += OnBoost;
    }

    void FixedUpdate()
    {
        CalculateGroundMovementSpeed();
        rb.velocity = appliedMovement;
    }
    #endregion

    #region Input Functions
    void OnEnable()
    {
        input.Enable();
    }

    void OnDisable()
    {
        input.Disable();
    }

    void OnMove(InputAction.CallbackContext context)
    {
        moveInput = context.ReadValue<Vector2>();
        movePressed = moveInput.x != 0 || moveInput.y != 0;
        appliedMovement.x = moveInput.x;
        appliedMovement.z = moveInput.y;
    }

    void OnJump(InputAction.CallbackContext context)
    {
        jumpPressed = context.ReadValueAsButton();
    }
    
    void OnBoost(InputAction.CallbackContext context)
    {
        boostPressed = context.ReadValueAsButton();
    }
    #endregion

    void CalculateGroundMovementSpeed()
    {
        if (boostPressed){
            appliedMovement.x *= standardSpeed * boostSpeed * Time.deltaTime;
            appliedMovement.z *= standardSpeed * boostSpeed * Time.deltaTime;
        }
        else{
            appliedMovement.x *= standardSpeed * Time.deltaTime;
            appliedMovement.z *= standardSpeed * Time.deltaTime;
        }
    }

    #region Collision Functions
    private void OnCollisionEnter(Collision collision)
    {
        if (collision.gameObject.tag == "ground")
        {
            appliedMovement.y = groundedGravity;
        }
    }
    #endregion
}

Here are the details in the inspector.

If you need any more details, please let me know.
Thank you for your time.

Just solved my own problem. I had too many things open and over half my ram was being used. After I restarted my computer, it cleared up and worked as expected. I didn’t consider it because everything else was working smoothly, but lesson learned.